1. Technical Field of the Invention
The present invention relates to a transmission of a vehicle, and more particularly to a transmission of a vehicle which is provided with change gears, and changes an engagement state of the change gears by utilizing a change drum having a cam groove in an outer peripheral surface, and executes a shift up and a shift down.
2. Prior Art
As a prior art of this kind of transmission, there is a transmission of a motor cycle disclosed in Japanese Unexamined Patent Publication No. 10-230894. The transmission is provided with a gear support shaft such as an input shaft, an output shaft or the like, a plurality of change gears, a shift fork changing an engagement state of the change gears, a change drum moving the shift fork in an axial direction of the gear support shaft, a change shaft rotationally operated at a predetermined angle via a change lever by a rider, and a change operation force transmitting mechanism transmitting the rotation of the change shaft at the predetermined angle to the change drum.
FIG. 15 is a schematically perspective view of a change lever (a change pedal) 301, a change shaft 302, a change drum 303, a plurality of shift forks 305 and a change operation force transmitting mechanism 310 in accordance with the prior art. FIG. 16 is an enlarged view of a cross section cutting the change operation force transmitting mechanism 310 in FIG. 15 along a surface perpendicular to an axial core O1 of the change drum 303, and FIG. 17 is an enlarged view of a cross section along a line XVII-XVII in FIG. 16. FIG. 18 is a side elevational view of a pole 316.
In FIG. 15, the change lever 301 is provided in one end of the change shaft 302 so as to be integrally rotatable, and a first sector gear 315 is provided in the other end of the change shaft 302. When the rider pushes up or pushes down the change lever 301, the change shaft 302 and the first sector gear 315 rotate in a direction of U1 or a direction of Dl at a predetermined angle. A plurality of cam grooves 311 are formed in an outer peripheral surface of the change drum 303, and each of engagement pins 305a of the shift forks 305 is engaged with each of the cam grooves 311. The shift fork 305 is selectively moved in an axial direction on the basis of a cam operation of the cam groove 311 by rotating the change drum 303 in a direction of U2 or a direction of D2 at a predetermined angle, thereby an engagement state of change gears (not shown) is changed.
The change operation force transmitting mechanism 310 comprises a driven ring 312 fixed to an end surface of the change drum 303 so-as to integrally rotate with the change drum 303, a pole holder 313 accommodated within the driven ring 312 so as to be relatively rotatable with respect to the driven ring 312, a pair of poles 316 held to the pole holder 313, a second sector gear 314 fixed to the pole holder 313 so as to be integrally rotatable and engaging with the first sector gear 315, and the first sector gear 315.
In FIG. 16, six concave portions 320 are formed in an inner peripheral surface of the driven ring 312 at a uniform interval in a peripheral direction, and a pair of semicircular concave portions 321 is formed in the pole holder 313. A pair of poles 316 are structured such that one of them corresponds to a pole for shifting up, the other of them corresponds to a pole for shifting down, and a base end of each of the poles 316 is formed in a semicircular shape, and is held to the concave portion 321 so as to be rotatable around a pole support point O3. The pole 316 rotates around the pole support point O3 between a disengaged state (a state in FIG. 16) in which the pole 316 is not engaged with the concave portion 320, and an engaged state in which a leading end of the pole 316 protrudes to an outer side in a diametrical direction so as to be engaged with any one of the concave portions 320. Each of the poles 316 is pushed to the engaged state by a push rod 331 and a spring 332 accommodated in a spring accommodating hole 330 of the pole holder 313. In this case, as shown in FIGS. 17 and 18, a leading end of the push rod 331 is fitted to a groove 316a formed in a leading end portion of the pole 316.
In the conventional structure mentioned above, for example, in the case of shifting up from any position of first speed to fifth speed, the change shaft 302 and the first sector gear 315 are rotated in the direction U1 by pushing up the change lever 301, whereby the second sector gear 314 and the pole holder 313 are rotated in the direction of U2 at a predetermined angle.
In FIG. 16, the lower pole 316 is engaged with the concave portion 320 of the driven ring 312 on the basis of the rotation of the pole holder 313 in the direction of U2 at a predetermined angle, thereby rotating the change drum 303 in FIG. 15 in the direction of the arrow U2 at the predetermined angle, and shifting up the engaged state of the change gears via the shift fork 305.
As shown in FIG. 16, in the support structure of the pole 316, in which the semicircular base end of the pole 316 is only fitted to the semicircular concave portion 321 of the pole holder 313, the following problem is generated. In other words, when the pole holder 313 is returned to the original position in the direction of D2 with respect to the driven ring 312 in a resting state, after the shift-up operation, the pole 316 is returned in a state in which the leading end is brought into pressure contact with an inner peripheral surface of the driven ring 312. Accordingly, there is applied a force intending to pull the pole 316 out of the concave portion 321 of the pole holder 313 on the basis of a frictional resistance between the inner peripheral surface of the driven ring 312 and the leading end of the pole 316, whereby the pole 316 does not smoothly move in the direction D2, and rattles or slants. In other words, it is hard to smoothly execute a returning process after finishing the shift-up operation. The same matter is applied to the returning process after the shift-down operation. Further, with respect to the remaining pole 316 which is not engaged with the concave portion 321 at a time of the shift-up operation or the shift-down operation, in a pair of poles 316, the “force intending to pull out” is applied just after the shift-up or shift-down operation is started.